全文获取类型
收费全文 | 20941篇 |
免费 | 1825篇 |
国内免费 | 920篇 |
专业分类
化学 | 3385篇 |
晶体学 | 113篇 |
力学 | 2091篇 |
综合类 | 136篇 |
数学 | 379篇 |
物理学 | 4297篇 |
综合类 | 13285篇 |
出版年
2024年 | 83篇 |
2023年 | 255篇 |
2022年 | 462篇 |
2021年 | 483篇 |
2020年 | 529篇 |
2019年 | 473篇 |
2018年 | 424篇 |
2017年 | 667篇 |
2016年 | 663篇 |
2015年 | 864篇 |
2014年 | 1026篇 |
2013年 | 1705篇 |
2012年 | 1200篇 |
2011年 | 1210篇 |
2010年 | 913篇 |
2009年 | 1053篇 |
2008年 | 942篇 |
2007年 | 1227篇 |
2006年 | 1098篇 |
2005年 | 995篇 |
2004年 | 958篇 |
2003年 | 811篇 |
2002年 | 725篇 |
2001年 | 631篇 |
2000年 | 522篇 |
1999年 | 528篇 |
1998年 | 428篇 |
1997年 | 368篇 |
1996年 | 329篇 |
1995年 | 340篇 |
1994年 | 279篇 |
1993年 | 276篇 |
1992年 | 214篇 |
1991年 | 170篇 |
1990年 | 174篇 |
1989年 | 169篇 |
1988年 | 169篇 |
1987年 | 90篇 |
1986年 | 60篇 |
1985年 | 46篇 |
1984年 | 26篇 |
1983年 | 5篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 7篇 |
1979年 | 19篇 |
1978年 | 5篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
A new flow electrical conductance instrument was constructed and tested on dilute NaCl solutions up to 458 K, and on more
concentrated solutions (maximum 0.436 mol⋅kg−1) at 373 K. The results of the new instrument agreed with those of previous authors within the estimated experimental errors.
The model of Bernard et al. (J. Phys. Chem. 96, 3833–3840 (1992), MSA) was found to represent the high-temperature results without introducing an ion-pairing equilibrium constant. The Fuoss–Hsia
conductance equation as given by Fernandez-Prini was found to represent the dilute concentrations with Λ° (NaCl) as the only adjustable parameter. It was found that Λ° (NaCl) could be expressed as a function of solvent viscosity and density by using three parameters found by regression of
literature results between 278.15 and 523 K. This equation along with the FHFP theory permits the equivalent conductivity
of dilute sodium chloride solutions to be calculated within the accuracy of the existing experimental measurements. 相似文献
112.
史振云 《科技情报开发与经济》2005,15(24):258-260
以博茨瓦纳帕塞公路工程施工为例,详细介绍了高等级公路水泥稳定土的施工准备、工艺流程与技术要求,指出了施工中应注意的问题。 相似文献
113.
研究以水泥处理固体有机物时,有机物对水泥水化的影响。以膜流模式说明水份在水泥浆体内传输的现象。水膜存在半干之水泥浆体,其厚度小于100nm,膜流由离分压所驱动,而离分压来自分子间作用力。膜拟结果发现,水泥浆体内局部位置可用以进行水化之水量为Q=-Aslv/6vπ。当有机物添加在水泥浆体内时,会影响Hamaker常数,Aslv因此可能使膜流不稳定或完全抑制膜流,因而使水泥浆体内局部缺水,影响水化进行,造成成品强度降低,影响品质。 相似文献
114.
The impoverishment of soil nutrients of nine gully head areas in Yuanmou Basin is assessed through an integrated evaluation method established on the basis of Fuzzy mathematics and multivariate mathematical theory. Results show that soil erosion of gully erosion area in Yuanmou basin has resulted in severe impoverishment of soil nutrients. All gully head areas are at high leves of impoverishment except for one at middle. By probing into and analyzing the mechanism of impoverishment of soil nutrients, we find that soil erosion has led to impoverishment of soil nutrients in a way of compacting soil, heightening position of obstacle horizon, and reducing the content of organic matter, as well as the direct loss of nutrient elements. Finally, this paper points out that soil and water conservation arming at the prevention of soil erosion is the most effective way against impoverishment of soil nutrients in Yuanmou basin. 相似文献
115.
Nak-Jin Seong Young-Hun Jo Myung-Hwa Jung Soon-Gil Yoon 《Journal of magnetism and magnetic materials》2006
Epitaxial Ti0.97Co0.03O2:Sb0.01(TCO:Sb) films were deposited on R-Al2O3 (1 1 0 2) substrates at 500 °C in various deposition pressures by pulsed laser deposition. The solubility of cobalt within the films increases with decreasing deposition pressure at a deposition temperature of 500 °C. The TCO:Sb films deposited at 5×10−6 Torr exhibit a p-type anomalous Hall effect having a hole concentration of 6.1×1022/cm3 at 300 K. On the other hand, films deposited at 4×10−4 Torr exhibits an n-type anomalous Hall effect having an electron concentration of about 1.1×1021/cm3. p- or n-type DMS characteristics depends on the change of the structure of TCO:Sb films and the solubility of Co is possible by controlling the deposition pressure. 相似文献
116.
The solubility and diffusion coefficient of carbon dioxide in intermediate‐moisture starch–water mixtures were determined both experimentally and theoretically at elevated pressures up to 16 MPa at 50 °C. A high‐pressure decay sorption system was assembled to measure the equilibrium CO2 mass uptake by the starch–water system. The experimentally measured solubilities accounted for the estimated swollen volume by Sanchez–Lacombe equation of state (S‐L EOS) were found to increase almost linearly with pressure, yielding 4.0 g CO2/g starch–water system at 16 MPa. Moreover, CO2 solubilities above 5 MPa displayed a solubility increase, which was not contributed by the water fraction in the starch–water mixture. The solubilities, however, showed no dependence on the degree of gelatinization (DG) of starch. The diffusion coefficient of CO2 was found to increase with concentration of dissolved CO2, which is pressure‐dependent, and decrease with increasing DG in the range of 50–100%. A free‐volume‐based diffusion model proposed by Areerat was employed to predict the CO2 diffusivity in terms of pressure, temperature, and the concentration of dissolved CO2. S‐L EOS was once more used to determine the specific free volume of the mixture system. The predicted diffusion coefficients showed to correlate well with the measured values for all starch–water mixtures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 607–621, 2006 相似文献
117.
Microstructure and related properties of hydrogenated silicon samples, Si:H, treated at high-temperature (HT) up to 1270 K under hydrostatic argon pressure (HP) up to 1.1 GPa are investigated. To prepare Si:H, Czochralski grown 0 0 1 oriented single crystalline Si wafer with 50 nm thick surface SiO2 layer was heavily implanted with hydrogen using the immersion plasma source of hydrogen ions with energy 24 keV.The surface of HT-HP treated Si:H was characterised by scanning electron microscopy. Reflectivity pattern measurements in the wavelength range of 350-2000 nm have been performed to analyse their surface and bulk properties. The volume averaging method for a model of layer-like structure has been used to simulate the HT-HP treated Si:H. The analysis of Si:H samples suggests the multi-layer structure composed of Si, Si:H, SiO, SiO2, and of porous Si layers in the sub-surface region. The porous Si:H samples model is in good consistency with experimental data from reflectance measurements. 相似文献
118.
详细阐述了省道002线分水岭到仲宫段跨越地带地层的时代、岩性,划分了岩、土的工程类别,为道路和桥梁设计、支挡物设置及工程概算提供了依据。 相似文献
119.
郭永盛 《山东师范大学学报(自然科学版)》1993,8(4):1-5
我们依据第四纪地质、考古和历史自然地理学资料,通过分析山东各类土壤母质的形成时期,推论各类土壤的成土年龄。认为一般情况下,山东土壤的年龄不大于2400年。 相似文献
120.